diff --git a/phpBB/config/services.yml b/phpBB/config/services.yml
index 4de47f750f..3bd9182924 100644
--- a/phpBB/config/services.yml
+++ b/phpBB/config/services.yml
@@ -170,6 +170,7 @@ services:
             - @dbal.conn
             - @config
             - @filesystem
+            - @user
             - %tables.ext%
             - %core.root_path%
             - %core.php_ext%
diff --git a/phpBB/includes/acp/acp_extensions.php b/phpBB/includes/acp/acp_extensions.php
index 88b6a9c270..3d3cfb7f16 100644
--- a/phpBB/includes/acp/acp_extensions.php
+++ b/phpBB/includes/acp/acp_extensions.php
@@ -70,7 +70,7 @@ class acp_extensions
 		// If they've specified an extension, let's load the metadata manager and validate it.
 		if ($ext_name)
 		{
-			$md_manager = new \phpbb\extension\metadata_manager($ext_name, $config, $phpbb_extension_manager, $template, $phpbb_root_path);
+			$md_manager = new \phpbb\extension\metadata_manager($ext_name, $config, $phpbb_extension_manager, $template, $user, $phpbb_root_path);
 
 			try
 			{
diff --git a/phpBB/includes/functions_admin.php b/phpBB/includes/functions_admin.php
index 3000a18668..2d3ac62f86 100644
--- a/phpBB/includes/functions_admin.php
+++ b/phpBB/includes/functions_admin.php
@@ -3030,7 +3030,7 @@ function get_remote_file($host, $directory, $filename, &$errstr, &$errno, $port
 				}
 				else if (stripos($line, '404 not found') !== false)
 				{
-					$errstr = $user->lang('FILE_NOT_FOUND',  $filename);
+					$errstr = $user->lang('FILE_NOT_FOUND', $filename);
 					return false;
 				}
 			}
diff --git a/phpBB/language/en/acp/extensions.php b/phpBB/language/en/acp/extensions.php
index e9f1c3ac5c..6ec722bb78 100644
--- a/phpBB/language/en/acp/extensions.php
+++ b/phpBB/language/en/acp/extensions.php
@@ -117,4 +117,7 @@ $lang = array_merge($lang, array(
 	'VERSIONCHECK_FORCE_UPDATE_ALL'		=> 'Re-Check all versions',
 	'FORCE_UNSTABLE'					=> 'Always check for unstable versions',
 	'EXTENSIONS_VERSION_CHECK_SETTINGS'	=> 'Version check settings',
+
+	'META_FIELD_NOT_SET'	=> 'Required meta field %s has not been set.',
+	'META_FIELD_INVALID'	=> 'Meta field %s is invalid.',
 ));
diff --git a/phpBB/language/en/common.php b/phpBB/language/en/common.php
index 5e524a6164..2020783100 100644
--- a/phpBB/language/en/common.php
+++ b/phpBB/language/en/common.php
@@ -231,6 +231,8 @@ $lang = array_merge($lang, array(
 	'FILESIZE'				=> 'File size',
 	'FILEDATE'				=> 'File date',
 	'FILE_COMMENT'			=> 'File comment',
+	'FILE_CONTENT_ERR'		=> 'Could not read the contents of file: %s',
+	'FILE_JSON_DECODE_ERR'	=> 'Failed to decode json file: %s',
 	'FILE_NOT_FOUND'		=> 'The requested file could not be found: %s',
 	'FIND_USERNAME'			=> 'Find a member',
 	'FOLDER'				=> 'Folder',
diff --git a/phpBB/phpbb/extension/manager.php b/phpBB/phpbb/extension/manager.php
index 0bfec23573..cd7289e085 100644
--- a/phpBB/phpbb/extension/manager.php
+++ b/phpBB/phpbb/extension/manager.php
@@ -26,6 +26,7 @@ class manager
 	protected $db;
 	protected $config;
 	protected $cache;
+	protected $user;
 	protected $php_ext;
 	protected $extensions;
 	protected $extension_table;
@@ -37,25 +38,27 @@ class manager
 	*
 	* @param ContainerInterface $container A container
 	* @param \phpbb\db\driver\driver_interface $db A database connection
-	* @param \phpbb\config\config $config \phpbb\config\config
+	* @param \phpbb\config\config $config Config object
 	* @param \phpbb\filesystem $filesystem
+	* @param \phpbb\user $user User object
 	* @param string $extension_table The name of the table holding extensions
 	* @param string $phpbb_root_path Path to the phpbb includes directory.
-	* @param string $php_ext php file extension
+	* @param string $php_ext php file extension, defaults to php
 	* @param \phpbb\cache\driver\driver_interface $cache A cache instance or null
 	* @param string $cache_name The name of the cache variable, defaults to _ext
 	*/
-	public function __construct(ContainerInterface $container, \phpbb\db\driver\driver_interface $db, \phpbb\config\config $config, \phpbb\filesystem $filesystem, $extension_table, $phpbb_root_path, $php_ext = 'php', \phpbb\cache\driver\driver_interface $cache = null, $cache_name = '_ext')
+	public function __construct(ContainerInterface $container, \phpbb\db\driver\driver_interface $db, \phpbb\config\config $config, \phpbb\filesystem $filesystem, \phpbb\user $user, $extension_table, $phpbb_root_path, $php_ext = 'php', \phpbb\cache\driver\driver_interface $cache = null, $cache_name = '_ext')
 	{
-		$this->container = $container;
-		$this->phpbb_root_path = $phpbb_root_path;
-		$this->db = $db;
-		$this->config = $config;
 		$this->cache = $cache;
-		$this->filesystem = $filesystem;
-		$this->php_ext = $php_ext;
-		$this->extension_table = $extension_table;
 		$this->cache_name = $cache_name;
+		$this->config = $config;
+		$this->container = $container;
+		$this->db = $db;
+		$this->extension_table = $extension_table;
+		$this->filesystem = $filesystem;
+		$this->phpbb_root_path = $phpbb_root_path;
+		$this->php_ext = $php_ext;
+		$this->user = $user;
 
 		$this->extensions = ($this->cache) ? $this->cache->get($this->cache_name) : false;
 
@@ -150,7 +153,7 @@ class manager
 	*/
 	public function create_extension_metadata_manager($name, \phpbb\template\template $template)
 	{
-		return new \phpbb\extension\metadata_manager($name, $this->config, $this, $template, $this->phpbb_root_path);
+		return new \phpbb\extension\metadata_manager($name, $this->config, $this, $template, $this->user, $this->phpbb_root_path);
 	}
 
 	/**
diff --git a/phpBB/phpbb/extension/metadata_manager.php b/phpBB/phpbb/extension/metadata_manager.php
index 047f0ca54c..5c4e8fbf00 100644
--- a/phpBB/phpbb/extension/metadata_manager.php
+++ b/phpBB/phpbb/extension/metadata_manager.php
@@ -36,6 +36,12 @@ class metadata_manager
 	*/
 	protected $template;
 
+	/**
+	* phpBB User instance
+	* @var \phpbb\user
+	*/
+	protected $user;
+
 	/**
 	* phpBB root path
 	* @var string
@@ -65,15 +71,17 @@ class metadata_manager
 	*
 	* @param string				$ext_name			Name (including vendor) of the extension
 	* @param \phpbb\config\config		$config				phpBB Config instance
-	* @param \phpbb\extension\manager	$extension_manager An instance of the phpBBb extension manager
-	* @param \phpbb\template\template		$template			phpBB Template instance
+	* @param \phpbb\extension\manager	$extension_manager	An instance of the phpBB extension manager
+	* @param \phpbb\template\template	$template			phpBB Template instance
+	* @param \phpbb\user 		$user 				User instance
 	* @param string				$phpbb_root_path	Path to the phpbb includes directory.
 	*/
-	public function __construct($ext_name, \phpbb\config\config $config, \phpbb\extension\manager $extension_manager, \phpbb\template\template $template, $phpbb_root_path)
+	public function __construct($ext_name, \phpbb\config\config $config, \phpbb\extension\manager $extension_manager, \phpbb\template\template $template, \phpbb\user $user, $phpbb_root_path)
 	{
 		$this->config = $config;
 		$this->extension_manager = $extension_manager;
 		$this->template = $template;
+		$this->user = $user;
 		$this->phpbb_root_path = $phpbb_root_path;
 
 		$this->ext_name = $ext_name;
@@ -141,7 +149,7 @@ class metadata_manager
 
 		if (!file_exists($this->metadata_file))
 		{
-			throw new \phpbb\extension\exception('The required file does not exist: ' . $this->metadata_file);
+			throw new \phpbb\extension\exception($this->user->lang('FILE_NOT_FOUND', $this->metadata_file));
 		}
 	}
 
@@ -154,18 +162,18 @@ class metadata_manager
 	{
 		if (!file_exists($this->metadata_file))
 		{
-			throw new \phpbb\extension\exception('The required file does not exist: ' . $this->metadata_file);
+			throw new \phpbb\extension\exception($this->user->lang('FILE_NOT_FOUND', $this->metadata_file));
 		}
 		else
 		{
 			if (!($file_contents = file_get_contents($this->metadata_file)))
 			{
-				throw new \phpbb\extension\exception('file_get_contents failed on ' . $this->metadata_file);
+				throw new \phpbb\extension\exception($this->user->lang('FILE_CONTENT_ERR', $this->metadata_file));
 			}
 
 			if (($metadata = json_decode($file_contents, true)) === null)
 			{
-				throw new \phpbb\extension\exception('json_decode failed on ' . $this->metadata_file);
+				throw new \phpbb\extension\exception($this->user->lang('FILE_JSON_DECODE_ERR', $this->metadata_file));
 			}
 
 			$this->metadata = $metadata;
@@ -224,12 +232,12 @@ class metadata_manager
 				{
 					if (!isset($this->metadata[$name]))
 					{
-						throw new \phpbb\extension\exception("Required meta field '$name' has not been set.");
+						throw new \phpbb\extension\exception($this->user->lang('META_FIELD_NOT_SET', $name));
 					}
 
 					if (!preg_match($fields[$name], $this->metadata[$name]))
 					{
-						throw new \phpbb\extension\exception("Meta field '$name' is invalid.");
+						throw new \phpbb\extension\exception($this->user->lang('META_FIELD_INVALID', $name));
 					}
 				}
 			break;
@@ -247,14 +255,14 @@ class metadata_manager
 	{
 		if (empty($this->metadata['authors']))
 		{
-			throw new \phpbb\extension\exception("Required meta field 'authors' has not been set.");
+			throw new \phpbb\extension\exception($this->user->lang('META_FIELD_NOT_SET', 'authors'));
 		}
 
 		foreach ($this->metadata['authors'] as $author)
 		{
 			if (!isset($author['name']))
 			{
-				throw new \phpbb\extension\exception("Required meta field 'author name' has not been set.");
+				throw new \phpbb\extension\exception($this->user->lang('META_FIELD_NOT_SET', 'author name'));
 			}
 		}
 
diff --git a/tests/dbal/migrator_test.php b/tests/dbal/migrator_test.php
index 381fe16115..4a1d15aea4 100644
--- a/tests/dbal/migrator_test.php
+++ b/tests/dbal/migrator_test.php
@@ -60,12 +60,14 @@ class phpbb_dbal_migrator_test extends phpbb_database_test_case
 
 		$container = new phpbb_mock_container_builder();
 		$container->set('migrator', $migrator);
+		$user = new \phpbb\user();
 
 		$this->extension_manager = new \phpbb\extension\manager(
 			$container,
 			$this->db,
 			$this->config,
 			new phpbb\filesystem(),
+			$user,
 			'phpbb_ext',
 			dirname(__FILE__) . '/../../phpBB/',
 			'php',
diff --git a/tests/extension/manager_test.php b/tests/extension/manager_test.php
index 6acade1e87..d9f8fbd1a4 100644
--- a/tests/extension/manager_test.php
+++ b/tests/extension/manager_test.php
@@ -101,6 +101,7 @@ class phpbb_extension_manager_test extends phpbb_database_test_case
 		$phpbb_root_path = __DIR__ . './../../phpBB/';
 		$php_ext = 'php';
 		$table_prefix = 'phpbb_';
+		$user = new \phpbb\user();
 
 		$migrator = new \phpbb\db\migrator(
 			$config,
@@ -121,6 +122,7 @@ class phpbb_extension_manager_test extends phpbb_database_test_case
 			$db,
 			$config,
 			new \phpbb\filesystem(),
+			$user,
 			'phpbb_ext',
 			dirname(__FILE__) . '/',
 			$php_ext,
diff --git a/tests/extension/metadata_manager_test.php b/tests/extension/metadata_manager_test.php
index 95544a6f7c..3678ac0a3f 100644
--- a/tests/extension/metadata_manager_test.php
+++ b/tests/extension/metadata_manager_test.php
@@ -77,6 +77,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 			$this->db,
 			$this->config,
 			new \phpbb\filesystem(),
+			$this->user,
 			'phpbb_ext',
 			$this->phpbb_root_path,
 			$this->phpEx,
@@ -97,7 +98,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e){}
 
-		$this->assertEquals((string) $e, 'The required file does not exist: ' . $this->phpbb_root_path . $this->extension_manager->get_extension_path($ext_name) . 'composer.json');
+		$this->assertEquals((string) $e, $this->user->lang('FILE_NOT_FOUND', $this->phpbb_root_path . $this->extension_manager->get_extension_path($ext_name) . 'composer.json'));
 	}
 
 	// Should be the same as a direct json_decode of the composer.json file
@@ -136,7 +137,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'name\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'name'));
 		}
 
 		try
@@ -147,7 +148,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'type\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'type'));
 		}
 
 		try
@@ -158,7 +159,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'license\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'license'));
 		}
 
 		try
@@ -169,7 +170,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'version\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'version'));
 		}
 
 		try
@@ -180,7 +181,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'authors\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'authors'));
 		}
 
 		$manager->merge_metadata(array(
@@ -197,7 +198,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Required meta field \'author name\' has not been set.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_NOT_SET', 'author name'));
 		}
 	}
 
@@ -224,7 +225,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Meta field \'name\' is invalid.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_INVALID', 'name'));
 		}
 
 		try
@@ -235,7 +236,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Meta field \'type\' is invalid.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_INVALID', 'type'));
 		}
 
 		try
@@ -246,7 +247,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Meta field \'license\' is invalid.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_INVALID', 'license'));
 		}
 
 		try
@@ -257,7 +258,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 		}
 		catch(\phpbb\extension\exception $e)
 		{
-			$this->assertEquals((string) $e, 'Meta field \'version\' is invalid.');
+			$this->assertEquals((string) $e, $this->user->lang('META_FIELD_INVALID', 'version'));
 		}
 	}
 
@@ -437,6 +438,7 @@ class phpbb_extension_metadata_manager_test extends phpbb_database_test_case
 			$this->config,
 			$this->extension_manager,
 			$this->template,
+			$this->user,
 			$this->phpbb_root_path
 		);
 	}
diff --git a/tests/functional/extension_acp_test.php b/tests/functional/extension_acp_test.php
index 8f0f9c6700..b6dd5db708 100644
--- a/tests/functional/extension_acp_test.php
+++ b/tests/functional/extension_acp_test.php
@@ -180,7 +180,7 @@ class phpbb_functional_extension_acp_test extends phpbb_functional_test_case
 	{
 		// test2 is not available (error)
 		$crawler = self::request('GET', 'adm/index.php?i=acp_extensions&mode=main&action=delete_data_pre&ext_name=test2&sid=' . $this->sid);
-		$this->assertContains('The required file does not exist', $crawler->filter('.errorbox')->text());
+		$this->assertContains($this->lang('FILE_NOT_FOUND', ''), $crawler->filter('.errorbox')->text());
 
 		// foo is not disabled (redirect to list)
 		$crawler = self::request('GET', 'adm/index.php?i=acp_extensions&mode=main&action=delete_data_pre&ext_name=vendor2%2Ffoo&sid=' . $this->sid);
diff --git a/tests/functional/metadata_manager_test.php b/tests/functional/metadata_manager_test.php
index 020e9cd142..080822d249 100644
--- a/tests/functional/metadata_manager_test.php
+++ b/tests/functional/metadata_manager_test.php
@@ -82,6 +82,6 @@ class phpbb_functional_metadata_manager_test extends phpbb_functional_test_case
 		$crawler = self::request('GET', 'adm/index.php?i=acp_extensions&mode=main&action=details&ext_name=not%2Fexists&sid=' . $this->sid);
 
 		// Error message because the files do not exist
-		$this->assertContains('The required file does not exist:', $crawler->filter('#main')->text());
+		$this->assertContains($this->lang('FILE_NOT_FOUND', ''), $crawler->filter('#main')->text());
 	}
 }
diff --git a/tests/test_framework/phpbb_functional_test_case.php b/tests/test_framework/phpbb_functional_test_case.php
index 0bfdfa57ac..182ffaaaf7 100644
--- a/tests/test_framework/phpbb_functional_test_case.php
+++ b/tests/test_framework/phpbb_functional_test_case.php
@@ -203,12 +203,14 @@ class phpbb_functional_test_case extends phpbb_test_case
 		);
 		$container = new phpbb_mock_container_builder();
 		$container->set('migrator', $migrator);
+		$user = new \phpbb\user();
 
 		$extension_manager = new \phpbb\extension\manager(
 			$container,
 			$db,
 			$config,
 			new phpbb\filesystem(),
+			$user,
 			self::$config['table_prefix'] . 'ext',
 			dirname(__FILE__) . '/',
 			$phpEx,